1 . Field of the Invention
The present invention generally relates to a semiconductor bare chip and a method of manufacturing the semiconductor bare chip and particularly relates to a mounting structure of the semiconductor bare chip, which allows reduced mounting area.
2 . Description of the Related Art
Because of the recent miniaturization of portable electronic devices, there is a need for a higher density when mounting a semiconductor on a mounting board. In order to achieve high-density mounting, a technology has been developed which utilizes the flip-chip method. With the flip-chip method, a semiconductor bare chip, which is a chip that is not packaged, is directly mounted on the mounting board. Thus, a reduced mounting area is achieved, since no additional area is necessary around the semiconductor bare chip.
FIG. 1 shows a partially enlarged view of a semiconductor bare chip 10 of the related art.
FIGS. 2A-2B are diagrams showing the semiconductor bare chip 10 of the related art which is mounted on a printed board 20.
As shown in FIG. 1, the semiconductor bare chip is constructed such that a stud bump 13 made of Au (gold) is formed on each electrode 12 on a bottom surface 11a of a semiconductor bare chip body 11 which has been cut-out from a wafer. The semiconductor bare chip is also constructed such that a conductive adhesive agent 14 is provided so as to cover the head of the stud bump 13.
The stud bump includes a seat 13a and a head 13b. The seat 13a has a shape of a squeezed sphere. The head 13b is substantially cylindrical. The head 13b has a diameter d2, which is smaller than a diameter d1 of the seat 13a. The head 13b protrudes from the seat 13a by a length a. The head 13b is formed so that a predetermined amount of conductive adhesive agent 14 will be provided thereon, and that the stud bump 13 can be easily pressed against an electrode 21 on a printed board 20.
As shown in FIG. 2A, the electrodes 21 are formed on the printed board 20. The electrodes 21 have a thickness b. The electrodes 21 have a rectangular shape with a side length c of approximately 40 .mu.m. The stud bumps 13 and the electrodes 21 are positioned so as to correspond to each other.
As shown in FIG. 2A, the semiconductor bare chip 10 is mounted using a flip-chip method of the press joint type. That is, the head 13b of the stud bump 13 is pressed against the electrode 21 and is stuck on the electrode 21 using the conductive adhesive agent 14. Also, the semiconductor bare chip body 11 is stuck on the printed board 20 by a thermosetting adhesive agent 31. Since the thermosetting adhesive agent 31 is provided within a gap 30 between the semiconductor bare chip body 11 and the printed board 20 and has been thermoset, the entire bottom surface 11a of the semiconductor bare chip body 11 is stuck on the printed board 20. Also, because the thermosetting adhesive agent 31 is thermoset and contracted, the entire bottom surface 11a of the semiconductor bare chip body 11 is pulled towards the printed board 20 with a force F1. With this force F1, the head 13b of the stud bump 13 is pressed against the electrode 21.
Here, the head 13b is formed such that a height a is approximately 30 .mu.m so that a sufficient amount of the conductive adhesive agent 14 adheres thereto.
The thickness b of the electrode 21 on the printed board 20 is reduced along with the refinement of the patterning, and is approximately 20 .mu.m.
The relationship between the height a of the head and the thickness b of the electrode 21 can be expressed as a&gt;b.
If the semiconductor bare chip 10 is displaced from the predetermined position when mounting the semiconductor bare chip 10 by the flip-chip method, the head 13b will slip off from the electrode 21 as shown in FIG. 2B. That is, the head 13b touches the top surface of the printed board 20 and the shoulder of the seat 13a does not come in contact with the electrode 21. Because of this, there will be no electrical connection between the stud bump 13 and the electrode 21.
In the following, a size which allows the semiconductor bare chip 10 to be displaced from a predetermined position P in either one of the directions X1 and X2 is referred to as an allowable size e. When mounting the semiconductor bare chip 10 by the flip-chip method, the allowable size e is determined such that the head 13b touches an edge of the electrode 21. The allowable size e is generally (c/2)+(d2/2), and is as small as approximately 30 .mu.m. This requires higher accuracy of a positioning process when mounting the semiconductor bare chip 10 by the flip-chip method. This makes it difficult to mount the semiconductor bare chip 10. Therefore, a problem arises that the possibility of poor mounting may occur and that of mounting production may be reduced.